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Ampmeter help

Discussion in 'Irrigation' started by EagleLandscape, Nov 16, 2007.

  1. EagleLandscape

    EagleLandscape LawnSite Platinum Member
    Male, from Garland, Texas
    Posts: 4,347

    I just bought an amp meter / multi meter deal for this xmas light install i have tomorrow. i had a regular multi meter, but nothing that could read amp load.

    its a sperry dsa-500

    I'm trying to read the amp draw on this power strip next to my desk, and I have it on the 40A setting (vs the 400A setting) and i have the line running through like the manual suggests, (line over left clamp, and under right clamp,) but im not getting a reading.

    am i missing something?
  2. DavidS1964

    DavidS1964 LawnSite Member
    Posts: 36

    You need a line seperator. Grainger has them for about $15.00.It splits your two main wires. The black or white wire. Once you spit the wires you can measure the amperage. You can also just add all of the appliances together. The amperage is written on the back of the appliance.

    P.S It is possible to use your other meter. You just kinda had to hold it in your hand.
  3. wab1234

    wab1234 LawnSite Member
    Posts: 48

    you can only have a single wire going thru the clamp, more than one and they cancel each other out similar to positive and negative charges with a magnet. the only way to use a meter without an amp clamp is to use ohms law. This states that amps equals volts divided by volts. I might have this backwards there is a book/bible called "UGLIES" which tells the true ohms law and everything else about the N.E.C. which might be helpful when doing any electrical work.
  4. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,308

    Ohm's Law -> I = V/R
    Units: I = Amps V = volts R = ohms

    Where a voltage of 1 V across a conductor causes a current of 1 A to the flow through it, resistance is 1 ohm
  5. wab1234

    wab1234 LawnSite Member
    Posts: 48

    Thank you kiril volts divided by volts doesn't make sense. I hope the rest was a little easier to understand
  6. DavidS1964

    DavidS1964 LawnSite Member
    Posts: 36

    W1234 you are incorrect about the only way is to use a multimeter with the clamp on ends for amperage. If you look at a regular meter without the clamp on ends there are some that have the current symbol on them. They will read amperage also. The current will pass through the leads. Usualy they are low current meter readers. Also if you have the wattage which is usualy on the back of all appliances and you know the voltage Dah!!. Voltage time amperage gives you wattage. So wattage dived by voltage gives you amperage.
  7. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,308

    The correct formula for determining electrical work is:

    W = IVt = (V^2/R)t = I^2Rt (where W is expressed as 1 Wattsecond = 1 Joule = 1 Nm)

    And for determining electrical power:

    P = V^2/R = I^2R (where P is expressed as watts)
    V = P/I

    As you can see in the second set of formulas, your method of determining wattage and voltage is incorrect.
  8. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,308

    Edit above -> your method is correct when using V = P/I where 1 V = 1 W/A.

    Sorry, got side tracked by the attitude and poor spelling.
  9. Ground Master

    Ground Master LawnSite Senior Member
    Posts: 505

    John - get a 2' long extension cord. Carefully cut off several inches of the outside cover to expose the 3 wires. You'll then be able to clamp on to 1 individual wire to read the amp load. Just be very careful with the exposed wiring

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